Certain spray guns or sprayers, including Models 43P and 43PA manufactured by Binks Manufacturing Company of Chicago, Ill., are adapted to spray low viscosity materials and include means for internally mixing components of material to be sprayed. The listed ones are of the airless, or hydaulically atomization, type, the Model 43P being a hand-held model, and the Model 43PA being adapted to be machine held as by a robotic arm. The latter model is particularly useful when it is desired to not only effect automatic positioning of the gun, but also where precise control over a spray pattern is particularly desirable or necessary. For example, the Model 43PA has been used to spray polyurethane or polyisocyanurate foam on both the inside and outside of the cylindrical cover which houses fuel and oxygen tanks of certain space vehicles. When spraying the outside of the cover, it is obvious that the coating must be even in order to provide an aerodynamically smooth surface. There are, of course, other, less exotic, instances where precision spraying is important.
For some time, difficulty has been experienced in achieving uniformity with conventional equipment. Accordingly, it is an object of this invention to provide an improved fluid control structure for a spray gun which will overcome the problem of variations in spray pattern presently experienced.